Analog to digital..something

Hi,

I have a client that want me to do something I could not imagine how to do.

They have a viscosity meter that will run a dosing pump. The meter is inputting an analog data, he want me to convert that to digital value directly running the motor.

How will I do that?

Please give me hint.

Without much detail it is difficult to determine just what you need.
Analog input modules generally operate on 0 - 10V or 4 - 20 mA. The value received is a digital representation of an analog value. You scale this value to the range of speeds that you want the motor run.

It may be the customer requires that you adjust the motor based on the readings and not directly use the value as the speed. I would get the range of allowable measurements from the meter, the range they will allow to continue running. Then scale this into the range of speeds that you have to run the motor,

Your drive would be required to accept a speed command over an I/O network of some type.

Say that your analog module give you a value of 0 to 32000 based on a range fom 4mA to 20mA. The speed range required is 200 to 1800 rpm. Divide the range of the input module by the range of speed to get you scaling.

32000 / 1600 = 20
Now your speed output integer will be the meter input value /20.

I mean binary, 1 (run) & 0 (stop). Let's say, if the meter inputs 6mA the motor should run for half a second. If it inputs 8 mA it will run for 0.75s, & so on.

I am not even sure if this condition is safe for a dosing pump. I have known magnetic motors to run @ least 2-3 mins before turning to stop.

Please advise me.

rikcando said:

Say that your analog module give you a value of 0 to 32000 based on a range fom 4mA to 20mA. The speed range required is 200 to 1800 rpm. Divide the range of the input module by the range of speed to get you scaling.

32000 / 1600 = 20
Now your speed output integer will be the meter input value /20.

Click to expand...

But they don't want to use inverter. If there is inverter, there will be DAC module. DAC module costs a lot, they want to cut it off.

We used to do a similar thing for filling transmissions. The scaling is the same only you scale to the time range and not the speed. There would be a range that is acceptable from the meter, and a given range of time based on these values. I am assuming it is a straight line conversion but you may need slightly more complicated math if it has a variance as the value goes up.

I am also assuming that the analog 6mA is input into a PLC through an analog module. This can be scaled as required.

From the example given, for each 1mA add .125 seconds to your base amount. Assuming the motor runs for .5 seconds on a minimum reading, and the meter gives you 9mA (5mA from minimum of 4mA) 5 x .125 = .625, run motor for 1.125 seconds.

What is the tolerance of the fill volume ? Are you using a peristaltic pump ? I'll admit that I have never worked with a hydraulic pump that I had to measure fluid viscosity to control the dispense cycle.

The filling volume is something missing right now. I will ask the end-user with regards to the volume they need to fill vs. the viscosity.

As for the pump, I do not know what type of pump they use. I am still waiting for a datasheet from them so I could check if its possible to incorporate the proportional control they want with it.